1. Technical Field
This invention relates to methods of signal processing for jet aircraft identification and, more particularly, processing reflected radar samples with multiple frequencies and random phases as if they were coherent.
2. Discussion
There exist several jet aircraft identification techniques that require long sequences of coherent radar samples to be collected and processed. For surveillance radar systems which employ rotating antenna arrays, it is often the case that insufficient time is available to collect this data on a single scan at a single transmitter frequency. Some of these systems are able to dwell on a target for longer periods by employing beam backscanning, which is accomplished by several transmitter frequency changes. Thus, the required time on target can then be attained. One of the consequences of beam backscanning at multiple frequencies is loss of signal phase coherence, which is critical to jet aircraft identification. Previous solutions to this problem have proven inadequate or impractical in that they severely degraded the radar system's acquisition and tracking functions, or have failed to re-establish signal coherence sufficiently to permit aircraft identification.
One possible technique involves slowing antenna scan rates considerably to attain the required time on target. The disadvantage of this solution is that search detection and acquisition probabilities are significantly reduced, and tracking performance is degraded to an unacceptable level. Another possible technique included multiple sensors and apertures dedicated to target identification. This solution has been deemed too costly to be marketable.